Signal seeking receiver



May 19 l'953 H. c. GooDRlcH, JR 2,639,373

SIGNAL sEExING RECEIVER Filed May 26, 194s ATTORNEY Patented May 19, 1953 SIGNAL SEEKING RECEIVER Hunter C. Goodrich, Jr., Collingswood, N. J., assignor to Radio Corporation of America, a corporation of Delaware Application May 26, 1948, Serial No. 29,267

(Cl. Z50-20) 8 Claims.

This invention pertains'to a radio receiver and more particularly to a radio receiver of the signal seeking type, wherein the tuning element of the receiver is driven by a tuning motor during the tuning process, thereby causing the receiver tuner to scan the frequency spectrum until a station is automatically selected.

Ordinarily, in operation of signal seeking radio receivers, when it is desired to tune in a station, a tuning motor is started to initiate the tuning process to cause the receiver to scan a particular frequency spectrum. When a signal of suiiicient strength is encountered, a portion of the received signal is applied to a control circuit which acts to remove the energy applied to the tuning motor, thereby causing the tuning operation to cease and permit the receiver to remain tuned to the particular received signal.

One of the problems heretofore encountered in providing a signal seeking superheterodyne radio receiver was that when the next station desired to be tuned in had a frequency allocation in close proximity to the station to which the receiver was tuned, it was necessary for the operator to .,iiick the starting switch by a quick actuation or series of quick actuations to prevent overriding the desired station during the tuning operation. Further, the tuning problem was aggravated by the necessity of keeping the starting switch closed, at least, until the tuner had scanned beyond the effective control range of the previously tuned station. This flicking techvnique is undesirable since experience has taught that a certain amount of skill and experience is required for tuning in the stations which have .frequency allocations relatively close to the station currently tuned in.

The present Iinvention contemplates overcoming this objection, and it is, therefore, an object of the present invention to provide a novel circuit including a gaseous control tube to permit a single actuation of the starting switch to automatically stop the receiver'on the next station having effective signal strength regardless of the proximity of its frequency allocation to the frequency of the currently tuned station.

It is a further object of the present invention to provide a signal seeking radio receiver which will automatically stop the tuning operation on the iirst received signal of adequate strength even though the starting switch is held in its actuated position.

It is a further object of the invention to provide a signal seeking radio receiver with a starting switchfor initiating the signal seeking operation, said switch having an initial starting position, to stop the receiver on the rst effective signal received regardless of the frequency allocation proximity to the previously received signal, said switch also having a continuous scanning position to continuously scan a band until the dial setting indicates the desired station isnearly reached, whereupon the starting switch may be released and the signal seeking functiony is completed automatically.

A further object of the invention is to provide a dual purpose starting switch having one position for automatically stopping the tuning operation on a station having a frequency allocation sufficiently close to the previous station that ordinarily a quick actuation, or flicking of the starting switch would be required, and a continuous scanning position of the starting switch for automatically stopping on a station having a frequency that would ordinarily-not require a quick actuation, or flicking of the starting switch.

Another object of the invention is to provide a novel signal seeking circuit wherein a single actuation of the starting switch, of any duration, will produce a blanking pulse of a predetermined duration to disable the control circuit until the tuner has scanned beyond the effective control range of the previously tuned station, whereupon normal signal seeking action is automatically restored.

A further object of the invention is to provide a signal seeking tuner having novel circuit means for momentarily reducing the receiver gain to improve the muting function during the switching operation.

Another object of the invention is to provide a signal seeking radio receiver having novel circuit means for muting the receiver by reducing the radio frequency (R. F.) and intermediate or beat frequency (I. F.) gain during the switching operation upon deenergization of the control relay, tlius preventing electrical transients created by the switching operation from causing an audible thud in the loudspeaker.

Further and other objects of the invention may be, and may become apparent, from a perusal of the disclosure herein. It is to be understood that while certain specific illustrations are presented, they are not to be considered as limitations except as defined by the spirit of the appended claims.

Referring to the drawings, the single gure shows a representative superheterodyne radio receiver circuit employing an antenna lll and a ground connection Il. shown by conventional symbols, inductively coupled by antenna transformer l2, having a primary i3 and a secondary I4, to the signal grid 9 of converter tube Vl. The output of converter tube VI is coupled through the I. F. transformer I5 to the input of the I. F. amplier tube V2. The output of I. F. amplifier V2 is coupled through the I. E. transformer .l5 to audio tube VS-'Which is a multi-purpose tube, and as shown, acts as audio amplifier, detector and AVC reotier. The amplified output of tube V3 is coupled through capacitor il to the input of audio output tube Vt. output tube Vd is connected to one end of the primary I9 of an output transformer it.

The other end of primary winding Slis con nected to a source of positive voltage denotl by the symbol B+. One side of 'secondarywndlng 2E of 'audio output transformer it is connectedv to the speaker or electrical transducer f2.3, the other end of secondary Winding Eil being connectedthrough a relay contact B and movable relay' contact arm BV to ground, completing the circuit'to speaker one side'of which is also ground-ed.y

Arm B together with other movable arms A and-'C form part of a control relay 2?. A fixed contact A' cooperates with arm A. Arno B is shiftable-between contact B' and another con tact B. Doublefthrow contacts'C and C cooperate similarly with arrnC. When the conu trolrelay'ZZ v'is deenergized Contact' sets fin-A', BL-B'", :and C-C yare closed, as shown in the drawings. lUpon lenergization of control relay 2E, contactset A-A is opened, Contact set B--B is opened.' and'contact vseth-B" is closed, while contact set C-C is opened and contact set C-C" is closed.y

Tol providev signal-seeking operation for the superheterodyne radio receiver, a tuning motor 255'is 'connected-by a shaft it to the tuner porm tionof the'radio receiver indicatedby variable condenser-s 27 and'.- While variable condens-- ers 'are shown specifically, it is to be understood that the shaft' may be connected to a permeability tuner lorany form of tuner which is adaptable for use in conjunction with the tuning motor.

Astarting'switchil, which is of the manually operable type, is indicated by the dotted line connecting contact arms D and E, which are movable yfrom-the normal rest position, wherein contact armfD engagesa fixed contact D and contact arm E'engages :a fixed contact E', to the initial starting position, wherein arms D andE are shifted respectively to contactsDf and E'.

A thirdposition-ofthe starting switch for conn t tinuous scanning is Yprovidedby stationary contacts D" and Ev". The starting switch is -of a typewherein a light-pressure on the connected movable armslD and E will shiftsaid-movable arms from theiirst, or restpositionf to the normally inoperative When the control tube relayl 22' is in` the. deenergized position as shown in thek drawings, indicating that the `receiver isv in playing position.

Uponmovement of. the startingiswitch to the second or initial starting position, control re` The plateiZl of 'audio lay 22 is energized by the flow of current from the B+ supply, through resistor 33, lead 34, contact set D resistor 35, and the winding of control `relay 22 to ground. Upon energization of the control relay, contact set A-A opens, placing a sensitivity `control 35 in series with the cathode returns to ground .of tubes Vl ,and V2. Also contact yset'B-B is opened, breaking the circuit from output transformer secondary 2t to speaker 2t and muting the radio receiver. The closure of contact se* B-B" completes the circuit betwecn tuning motor 25 and motor supply t?, energizing the tuning motor and causing the receiver to scan the frequency spectrum by virtue ofthe movement of variable capacitors 2'1 and ESL The closure of contact set C-C" completes a current path from the B| supply through .resistor 33, contact set C-C", resistor 3E', and the Win-ding of control relay 22 to ground, maintaining energization of the control relay when thestartingV switch 3l! has been-.released to` its rest position.

The closure oflcontact set C-C" applies that portion ofthe B+ voltage. that exists'across resistor 35' and control relay Winding 22, to the plate et ofrcontroltube Vt, placing said` tube in an operable condition. A portion offthe volton plate` Stof. tube-V6, is applied through resis-tor Se' to thescreenfd of BF() mixertube'V, causing thev BPO vmixer tube also to. become-op.- erative. When the receiver tuned. frequencyappreaches kthe frequency of asignal of .adequate strength, the resulting I. F. signal on theplate of V2 is impressed through .capacitor 'l on the signal grid of the BFG mixer VtiV Resistor 't provides a D. C. grid returnto ground.. Upon application of voltageto the screen'l of BF() mixer tube V5, the oscillator section of V5 compricing screen fic, yoscillator grid: 42,. andwcathode oscillates at a frequency determined by the values of inductor' and capacitor 4 l TheBFO frequency is made equal Lto the 1nominal receiver I. F. frequency. Capacitor:435couplesoscillator grid 42 to the tarnrcircuitcomposed of inductor 5 and capacitor M. Resistordiserves as .grid leak to theoscillator grid A2.

The application of ancI.l ikA signalv vtothe signal grid .ofV causes the BFG toeect a heterodyne action, and afrcquency component .equal tothe difference between the. frequency ofi.. F. signal and the frequency generated in thefoscillatoriscction of-.V appears. onthefplate 46': of tubclVS. This difference, or beat'.frequencyvsignal; is; coupled'byl capacitor @il to. ther control gridorthe tube In either the restingzor initial starting position'of starting switch .Ema cathode bias voltage from voltage sourcefxis applied l,tothe cathode 52 of `tube V6;

Tube V6 isbiasedbeyond.cut-offl sol thatit Willinot conduct or ire until apositivepsignal y.oi a certain .amplitude isapplied.tothe-control grid. Until the receiver tuned frequency; has .very,close lywapproached the frequencyfof thezssignal .torbe received, the' beatfrequency appearing onthe plate Mrof tube V5 will lbe relatively-high.. Since V5 has a relativelyv hghplate:resistance;a1high beat frequency Will bei largely, byepassedd to ground through the serieszpathof. capacitors 47, 48,' and 49. and-Willnot produceuiicient signal amplitude on controlgridiof V6:to.fcause iii-ing. The seriesccapac-itancef; of capacitors.V 4.1, 4S, Iand 49 in comparison with the-.platerresistance cf. V5;- isof'suc'h avalue-:thatonly relatively lotv4 beat frequencies, corresponding. to. :accurate receiver tuning for the particularsignalrwill produce suiilcie'nt'voltage attliepositive peak' ofth'e l. abruptly. 'When the starting switch is closed and the con- .troll relay vis energized, the opening of contact set '"CLC removes that portion of the B|l`voltage fformerly applied to terminal 60, which is conj beat frequency signal on the control grid of V6 to cause V6 to fire.

When the signal has been accurately tuned in to cause control tube V6 to fire, most of the current wvhichformerlyy flowed through resistor 35 in the winding kof'cor'itrol relay 22 to ground, Vis shunted throughiieadzes and pntecapathqqe 52, and voltage source'S` to ground. "Since the total current through contacts C-C is limited by the presence of resistor 33, the reduction in currentwAv portionV the receiver will automatically stop on ""the' neiit'fsignal of adequate strength regardless "effi whether ornotfithe starting switch has been flowing through the winding of control relaymZZ causes the relay to shift to the deene'rgizedposition. Upon deenergizationLoffthe,relaythgopening of contact set C-C" removes;the'A voltage ,from plate 38 of control tube V6, and from screen 48 of the BFO mixer tube Vzhmalii-ngbg hnQf these tubes inoperative, and also 'breaks the 'j rent flow through the winding of control relay 22.

The opening of contact set B- "deenergizes thetuning motorr 25, leaving the receiver prbper-ly tuned to, thelparticular..actuatingsignal. ,-The closure of l.contact set B -B' ,.,c'ircuit between the outpttransformer second- .'arywinding 20 andthespeaker 2 3. The ,closing l ,fo'fc'ontact set .A-A short circuits .the resistance Yintroduced by sensitivitycontrol 3 6 in thecathode ,returns of Vl and V2, restoring the receiver t jfull-sensitivity. .4

at At the instantthegcontrol tubefV fires, ,the v voltage on plate 38 of tube V6 falls suddenly'as-Jeo a result of v,the plate current of V6 passing completes the 4through resistor 33.- CapacitorV 53 is connected f from the plate38 of V6 to the AVC line 54 supplyfing AVC voltage to the control grids of the con-` .Yf verter .VI andthe I. Ramplier V2. The sudden dropAin-voltage onplate 38 of -VG atrthe instance .of.1'iring, causes a momentary negative ,pulse on AVC line 54, as capacitor 53 discharges through resistors 56 and 51. This momentarily lowers the gain of tubes VI and `V2 making the, receiver momentarily insensitive at that instant to any electrical-.transientsl produced by control relay 22 as its contacts move from the energized tothe .deenergizedposition Upon completion of, discharge ofycapacitor 53,the normal gain of the receiver is restored. The purpose of abovesaid .negative pulse is to prevent anyA electrical'trani1, sients caused bythe switchingwof thecontrol relay-from producing an audible thud in the speaker, and to cause the received signal to become audible somewhat gradually rather v than nected to the junction terminal 8 of capacitors 48 and 49. Capacitor 49 then discharges through resistor 58, and capacitor 48 discharges through resistor 58 and grid resistor 6l. The discharge current of capacitor 48 flowing through resistor 6| causes a momentary negative voltage pulse on the control grid of tube V6, which pulse is an increased negative bias on the control grid of V6 and prevents the beat frequency signal developed by the signal being received at the time the starting switch is closed, from causing the control tube V6 to fire. Resistor 6l is of such a value that the time constant of the control grid circuit of V6 causes the negative pulse to persist only for the length of time required for the receiver to scan out of the range of control of the previous incoming signal. The grid bias on tube 'V6 is thus restored to its normal value before the receiver has scanned to the next yfrequency rcontact sets D-D" and Ii! are closed, "the reception 'ofsigr'nal of suflicien't'strength to fire *fcontrol'ftube 'V'lwill cause control -rela'fy 22 to be deenergized 7as a'resultof the shuntirig effect of the plate circuit of V6.4 Thus when the starting vswitch hasbeen moved to the initial starting released-tothefrest position at the time the signjal is encountered. This prevents the receiver from'skipping any effective signal encountered Vbefretli'e' op''r'ato'r has released the starting lswitch.

' continuous scanning position, thatlis with contact sets D-D'f" and-Ee-'E closedywhichlopens the cathode circuit of control tube -V6,lan dpre Y vents --any unwantedV signals 1 from prematurely stopping thescanning action. -When-the desired ffrequency is approached, asobservedon--the tun- -fing -dial,the starting-switch maybe releasedto Apermit said switch to'restore to the rest-position, and the receivervwill then stop; automatically on the next signal-received. i A -From the foregoing, gitgwilll b e vseen--vthaltl` the starting switch is essentially dualv purpose -inthat an initial starting position@ofv the starting switch is provided so that once'the starting'switch is actuated to its initial starting"positionf'the'provision of the blankingpiilse permitsithe tlne to move beyond the rangef thfcurrently'tuled signal, andthe Itliyratr'on contact circuit permits thefirst signal received of ei'ectivestrength to cause the tuningl operati'o'hvto cease,v `even tliogh they starting switch is vheld in'theinitialfstarting "position Aby 'the operator. vCo'riseolu'ehtly'i,""iinder the condition'sQit will'be impossible for the uer to over-ride the iirst effective signal'received, ldue Yto the operator holding the switchinfthefinitial starting position too long. Therefore, l`r(agardless j of proximity of frequency? allocations; meerst new signalV v"of A'effective l' cause the "tuning operation'to cease. l

The continuous scanning position of tlidual purpose starting switch permits *thel tuner to override lall signals until theswitch is re1eased,thereafter, the tuner will cease operating onlreceipt of 'the firstsig'nal of 'eifectivestrength Anual muting'of"the"receiver is 'provided in that a momentary muting circuit momentarily reduces the receiver gain during the control tube operation to permit the new signal to increase at such a rate as to eliminate =a thud in the speaker, while another muting function is also performed to totally disable the speaker during energization of the tuning motor.

While specific circuits, and arrangement of parts, have been shown to illustrate the invention, it is to be understood that changes and modifications may be made therein without departing from the spirit of the invention as defined by the appended claims.

What is claimed is:

1. In a radio receiver of the heterodyne type including at least a frequency converter stage having at least an anode, a cathode, and a control grid and an intermediate frequency amplifier stage having at least an anode. a cathode, and a control grid connected in signal transfer relationship, the combination including rectifier means coupled to the output of said intermediate frequency amplifier for `deriving a biasing voltage from an intermediate frequency signal, an automatic voltage control line connected in circuit between said rectier and the control grids of said converter stage and said amplifier stage; signal tuning elements connected to said converter stage, a scanning system causing said tuning elements to scan va predetermined frequency range, control circuit ele-ments connected in said scanning system to terminate the scanning in respense to the reception of a signal of predetermined intensity,'and capacitive means coupling said control circuit to said automatic voltage ccntrol line whereby actuation of said control elernents applies a momentary negative pulse on said control line to lower the gain of said receiver.

2. The combination as defined oy claim l, wherein said control circuit elements include a gaseous tube and said capacitive means couples the anode of said tube to said automatic voltage control line.

3. In a signal seeking radio receiver system the combination comprising tuning means for said receiver, scanning means causing said tuning means to scan the tuning frequency spectrum until a station automatically selected, and control means for said scanning inea-ns including a gaseous discharge tube having at least an anode, a gridand a cathode, relay means connected in circuit with said cathode and anode ior actuating said scanning means, a resistor and capacitor connected in shunt between said grid and cathode, and switch means selectively applying a source of direct potential across said capacitor during the normal reception period of said ree ceiver, said switch means being actuated by said relay means upon initiation of said scanning means whereby said source is disconnected from said capacitor and said capacitor discharges through said resistor temporarily impressing a negative voltage pulse on said grid to maintain said tube non-conductive within the period required for said tuning means to scan away from the signal being received.

4. In a signal seeking radio receiver system the combination comprising tuning means for said receiver, scanning means causing said tuning means to scan the tuning frequency spectrum until a station is automatically selected, a starting switch for initiating operation of said scanning means upon actuation the cof from resting position to initial starting position, and control means for causing said tuner to stop on the first received signal of predetermined strength when said starting switch is in either the resting position or the initial starting position., said control means including a control tube having an input circuit actuated in response to signals oi predeterrn ed strength, a. control relay energized by said starting switch to initiate said scanning means, and a contact on said relay to hold the relay in an energized positions said control tube being connected in parallel with said relay to provide a low impedance path for the energizing current of said relay whereby said relay is cie-energized in response to actuation of said control tube at either the resting or initial starting position or the starting switch.

5. A system as donned in claim e, wherein continuou scanning' contacts are provided for said starting switch, and s. control tube is prevented from responding to said si r`nais in the continuous scanning position of ceiver sensi said control z y control means is provided, and is provide-:i with contacts which operate co, said control mean", in the energized r '-5 tion to reduce the gain of said receiver, whereby only signals oi a pre determined strength the tui to stop.

7. A system defined in clair e, including signal inuting contacts on said control relay to e said routing nieans in the energized positif 3. A system heat fre-( signal ci s a low freduenc r is provided, the output ncy oscillator being of 'i the signal of adequate strength is properly tuned, and the input circuit of the control ubc comprises a capacity voltage divider wherein the series capacitance of the voltn age divider is of such a value that only relatively low beat frequencies corresponding to accurate receiver tuning provides suilioient voltage to actuate the tube.

lfiUilTEE C. G-GODRICH, References Cite-d in the iile of this patent UNITED STATES PATENTS Number Name Date 2,835,175 ldcenna' Mar. '34, 1936 53,177,713 Grandi/ist Oct. 3l, 1939 Z22/,224 Hallam Bec. l0, 1940 2,364.13? l andrews Dec. 15, i942 2,326,737 Andrews Aug'. 1'7, 1943 2,387,5'i4 Usselinan Oct. 23, 19125 2,426,580 OBrlen Aug. 26, 1947 2,525,442 Bischoff Oct. l0, 1950 

